The present invention relates to a superconducting magnet apparatus suitable for a magnetic filed generation source of a magnetic resonance imaging apparatus.
A superconducting magnet apparatus used as a magnetic field generation source of a magnetic resonance imaging, for example, comprises a pair of cooling medium chamber enclosing a plurality of superconducting coils having different diameter and formed annularly, a pair of vacuum chamber enclosing each cooling medium chamber, and a connecting bar connecting each of the vacuum chambers so as to form a magnetic field space (measuring space) between the pair of vacuum chamber. Such apparatus is disclosed in Japanese Laid-open Patent Publication Hei-9-153408 and U.S. Pat. No. 6,580,346B1 corresponding to Japanese Laid-open Patent Publication Hei-9-153408.
Each cooling medium chamber includes main coil, counteracting coil, correction. coil forming superconducting coils, respectively. The main coils is composed by a supercondunting coil and generates high intensity magnetic field in the central region of the magnetic field space and generates uniform magnetic field higher than a predetermined level. The counteracting coil prevents the magnetic field generated by the main coil from leaking outside the vacuum chamber. The correction coil flows the current in same direction or reverse direction to that of the main coil and corrects the magnetic field by the main coil. In the MRI apparatus such as above described apparatus, it is required to form a high intensity static magnetic field in the imaging region so as to obtain diagnosis results together with a lot of information and clear image.